Tuesday, November 30, 2021




Silicon  Diode  is  the most  common   use   but   for some circuit   it   need  a  schottky   diode .   Schottky   diode  has  low voltage drop and fast recovery time so it can  operate  with high frequency application.   We  know  voltage drop across  Silicon Diode is  0.5-0.8V  and   0.1V - 0.45V  for   schottky   diode.   I  have sample of   both  1N5402 standard general  purpose Silicon Diode ,   1N5820    for  schottky   diode.  I  will measure it and  present  the result on this article.


1.   Silicon  Diode  Checking.
The voltage drop across  a  Silicon Diode is  0.5-0.8V  and   on   photo  =  0.528V

     Forward  bias   of   1N5402   Silicon  Diode.

For  analog multimeter  you  can use LV scale to check the voltage drop  across Silicon Diode as show below.  Set   knob  to  Rx1 range and make  zero ohm adjustment to get the accuracy value before using  LV scale.   At  LV scale there is  0 , 1 , 2 , 3   scale  and   this case from photo below  the measured value is  around   0.7V

Use  LV scale to check voltage drop across 1N5402   Silicon Diode.  Use  Rx1 range  and read value  from LV scale.   On this example is  around   0.7V

The  Silicon Diode  has  no leakage current  ,  on   photo use analog multimeter Rx1 range  Function as  3VDC  150mA current source and  use  digital multimeter to measure leak current , the digital multimeter   show  no leadkage current when applying  reverse bias   then reverse the test leads ,  connect diode as forward bias there is   some  current flow  103.9mA.

No current flow ( Reverse Bias  of   Silicon Diode )

   Current  flow ( Forward  Bias of   Silicon Diode )

2.  Schottky   diode  Checking.
     Schottky   diode  has    0.1V - 0.45V  drop across it.   This case on photo below  the measured  value  is  0.123V  (  part number   1N5820  Schottky   diode   ).

     Example of  voltage drop across   Schottky   diode.

When  applying  reverse  bias to Schottky  diode there is  some leakage current ,  this case we get measured current value   31.7uA  ( part number   1N5820  ).    I   use  current  source from Rx1 = 150mA  3VDC  ( test function from  analog multimeter).

3.    Unknown type of  diode
Part  number  MUR820  (U820)  on  datasheet   give information  as  Ultrafast  Diode.
I test   and  get measured value  as  0.426V voltage drop across ( when applying forward bias )  and  no leakage current when applying reverse bias   so  I think   it   should   be  Silicon Diode  type.

   There is  not   leakage current when applying  reverse bias to  MUR820.  There may be much  small amount as nA   so  standard  Digital multimeter can not measure  it.